This project proposes to develop drugs for treating opportunistic infections by Candida in AIDS patients. Because of the impaired immune system, AIDS patients are particularly susceptible to opportunistic infections by yeast (or fungi), which occur in up to 81 % of the patients. Yeast-like fungi of the genus Candida, including C tropicalis, C albican, and C parapsilosis, are the most common occurring infections. A direct relationship between the secretion of extracellular acid proteases and the virulence of these strains has been established. Evidence supports the contention that the inhibition of the Candida proteases lead to the inhibition of spreading of Candia infection. To design and test protease inhibitor drugs for Candida infection, the applicant has synthesized and purified the recombinant protease called canditropsin from C. tropicalis. Two other recombinant proteases, candialbisin and candiparapsin, from C albican and C parapsilosis will also be prepared. The specificities of these three proteases at each of the 8 subsites will be determined using protein and synthetic peptides. The subsite specificity information will be used to design, synthesis, and test transition-state analogue inhibitors for these three proteases. Canditropsin has been crystallized and the x-ray crystallographic structure is under investigation by a collaborator. The structures of protease-inhibitor complexes will be investigated in order to understand the interaction between the enzymes and the inhibitors. This information will be used to design the second generation inhibitors.